Radial piston pump



Sept. 8, 1970 w. H. DIETER ET AL 5 5 RADIAL PISTON PUMP Filed March 13, 1968 5 Sheets-Sheet l INVENTORS. Werner H- DlcTck Horst KRAMER p 1970 w. H. DIETER ET A 3,527,547

RADIAL PISTON PUMP Filed March 13, 1968 3 Sheets-Sheet 2 1 31 -31 1'2! I 5 I 2 10 /a a 34 ea "-35 lNVENTORS:

W rner H D\eTer Horst KRAMER p 1970 w. H. DIETER ET AL 3,527,547

RADIAL PISTON PUMP Filed March 13, 1968 3 Sheets-Sheet 5 FIG. 4 34 INVENTORS Werner H DIeLer HOIS) KRAMER 3,527,547 RADIAL PISTON PUMP Werner H. Dieter and Horst Kramer, Lohr (Main), Germany, assignors to G. L. Rexroth GmbH, Lohr (Main), Germany Filed Mar. 13, 1968, Ser. No. 712,718 Claims priority, applicatiogr Germany, Mar. 15, 1967,

R 4 ,50 Int. Cl. F04b 1/04, 21/02, 23/04 US. Cl. 417203 1 Claim ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The present invention relates to radial piston pumps for hydraulic systems. More particularly, the invention relates to improvements in radial piston pumps of the type wherein a rotary eccentric cooperates with springs to effect radial movements of pistons in the respective cylinder blocks and to thereby compel a liquid to flow from an inlet to one or more outlets.

Conventional radial piston pumps are not self-priming because dead spaces in the heads of cylinder blocks are too large in relation to the displacement of pistons. Thus, when a piston performs a suction stroke, the resulting suction is insufficient to move the spring-biased suction valve in the respective cylinder block away from its seat. Therefore, conventional radial piston pumps must be primed prior to use. Furthermore, and in order to insure satisfactory lubrication of bearings and of the ring which is mounted on the eccentric of the pump shaft to reciprocate the pistons, the housing of a conventional radial piston pump must be installed in an oil-containing sump or directly in the oil tank of the hydraulic system. Still further, and if the pump is not installed in the sump or tank, its inlet must receive oil by gravity feed. When the diameter of pistons in a conventional radial piston pump is small, and if the pump must furnish oil at a very high pressure, the viscosity of oil must be very low (for example, l.4 E/50 C.) which reduces the output at elevated pressures and results in unsatisfactory lubrication of moving parts.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a radial piston pump which is self-priming and wherein the moving parts are lubricated in automatic response to operation of the pump.

Another object of the invention is to provide a radial piston pump which can suck a hydraulic pressure medium without necessitating admission of such medium by gravity flow and which can insure highly satisfactory lubrication between the pistons and the parts which move the pistons radially without necessitating installation of the pump in an oil tank or sump.

A further object of the invention is to provide'a simple centrifugal pump which forms part of the improved radial piston pump and which invariably insures entry of liquid United States Patent into the chambers of cylinder blocks in response to rotation of the pump shaft.

In accordance with a feature of the invention, the improved radial piston pump comprises a housing defining a compartment and having a liquid-admitting inlet, a driven shaft journalled in the housing and having an ec centric thereon, a centrifugal pump driven by the shaft and arranged to draw liquid from the inlet into the compartment, a cylinder block provided on the housing and having an outlet and conduit means connecting the outlet with the compartment, a normally closed suction valve provided in the conduit means to seal the compartment from the outlet, and a piston received in the block and reciprocable by the eccentric to intermittently open the valve and to effect the fiow of liquid from the compartment into the outlet. The centrifugal pump preferably comprises an impeller mounted on the shaft and arranged to deliver liquid all the way to the valve in the conduit means so that the pressure of liquid assists the piston in opening the valve when the piston performs a suction stroke.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved pump itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of a specific embodiment with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an end elevational view of a radial piston pump which embodies the invention;

FIG. 2 is a side elevational view as seen in the direction of arrow A in FIG. 1;

FIG. 3 is an enlarged sectional view as seen in the direction of arrows from the line III-III of FIG. 2; and

FIG. 4 is a larger scale view of a detail in the structure of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT The pump which is shown in FIGS. 1 to 4 comprises a housing 1 which is airand liquid-tightly connected with three cylinder blocks 2 by screws 3. The housing 1 accommodates a portion of a driven shaft 4 which is rotatable therein in antifriction bearings 5 and 6. An eccentric 7 of the shaft 4. is mounted in an antifriction bearing 8 having an outer race or ring 9 which can displace the pistons 10. The radially innermost end of each piston 10 is provided with a split ring 11 which serves as a stop for a dished retainer 12. Helical springs 13 operate between the retainers 12 and shoulders 2a of the respective cylinder blocks 2. The springs 13 bias the pistons 10 against the outer race 9 of the bearing 8.

The head of each cylinder block 2 is provided with internal threads to take an externally threaded sleeve 14 defining an annular valve seat 15 for a disk-shaped suction valve 16 adjacent to the outer end of the respective piston 10. Valve springs 17 bias the valves 16 against the respective seats 15. The springs 17 are accommodated in suction chambers 18 defined by the respective cylinder blocks 2, and these chambers 18 are in communication with bores or passages 19 which are normally closed by one-way ball valves 20 biased by helical springs 23. The ball valves 20 normally seal the passages 19 from passages 22 latter which extend into outlets 21 and 21'. The outlets 21' are sealed by threaded plugs 21a shown in FIGS. 1 and 2. The springs 23 which bias the ball valves 20 against the seats at the outer ends of passages 19 abut against retainer screws 24 threaded into the blocks 2.

One end of the eccentric 7 is adjacent to a flange 25 which holds the bearings and 9 against axial movement and is provided with radial or tangential channels 26 communicating with an axial bore 27 of the shaft 4. The flange 25 constitutes an impeller of a centrifugal pump which draws liquid into a compartment 35 of the housing 1 whence the liquid flows toward the suction chambers 18. The impeller 25 is eccentric with reference to the axis of the shaft 4 to balance the eccentric 7. The compartment 35 is sealed by a gasket 28 which surrounds a portion of the shaft 4. The liquid is admitted by way of an inlet 29 which is sealingly afiixed to the housing 1 by screws 30.

The pistons are reciprocable in bores 31 of the cylinder blocks 2 and these blocks are further provided with bores 32 which are parallel to the bores 31 and communicate with registering bores 32a of the housing 1 (see FIG. 1). The bores 32, 32a connect the compartment 35 with spaces 33 at the outer sides of suction valves 16. The spaces 33 are sealed by covers or caps 34 which are secured to the remaining or main portions of the respective cylinder blocks 2 by aforementioned screws 3.

Each bore 32a can be said to form part of the compartment 35 in the housing 1. The bores 32, spaces 33, suction chambers 18 and passages 19, 22 form three conduits which connect the compartment 35 with the respective outlets 21 or 21' and each of which accommodates one of the normally closed suction valves 16.

The'operation is as follows:

One end of the shaft 4 (namely, the upper end, as viewed in FIG. 2 or 3) is coupled to the output member of an electric motor or other suitable prime mover, not shown, so that the eccentric 7 moves the pistons 10 by way of the outer race 9 of the bearing 8. The impeller 25 rotates with the shaft 4 and its radial or tangential channels 26 draw liquid from a source by way of the inlet 29 and axial bore 27. Such liquid flows into the compartment 35 which is in communication with the bores 26. From the compartment 35, the liquid flows through the bores 32a and into the conduits including the bores 32 and spaces 33, i.e., to the outer sides of suction valves 16. When a piston 10 performs a suction stroke (i.e., radially inwardly toward the shaft 4), suction develops in the respective chamber 18 and such suction overcomes the bias of springs 17 so that the respective valve 16 moves away from its seat and admits liquid into the chamber 18. The liquid fills the suction chamber 18 and opens the ball valve when the respective piston 10 thereupon performs an outward stroke, i.e., away from the shaft 4. The suction valve 16 is then closed by its spring 17 and also by pressure of liquid in the suction chamber 18. The liquid which passes beyond the ball valve 20 flows into the passage 22 and outlet 21.

In order to improve the etficiency of the pump, the impeller 25 may be made in the form of a turbine wheel with buckets. However, it was found that a simple impeller with radial or tangential channels 26 can produce a sutficient head for nearly all applications of the pump.

An important advantage of the improved radial piston pump is that the impeller 25 causes the liquid to flow from the inlet 29 into the compartment and all the way to the outer sides of suction valves 16 in the cylinder blocks 2. When the pistons 10 perform suction strokes under the bias of their springs 13, the pressure produced by impeller 25 assists the suction in chambers 18 to insure opening of valves 16 and resulting How of liquid to the outlet or outlets. When the pump is started, the liquid which is drawn into the chambers 18 invariably expels air to insure automatic priming. Furthermore, and

since the liquid which flows to the spaces 33 invariably flows through the compartment 35, such liquid lubricates the bearings 5, 6, 8 and the external surface of the race 9. Contrary to the mounting of conventional radial piston pumps, the liquid need not flow from a tank directly to the spaces 33 which are adjacent to the suction valves 16 so that, and if the novel pump is installed in a tank, the quantity of useful liquid in the tank is much higher than in conventional pumps. The improved pump can operate with liquids of relatively high viscosity (for example 4.5- 10 E/ C.) even if the diameters of pistons 10 are relatively small. The output and the volumetric efiiciency of the pump are very satisfactory, even at high rotational speeds of the shaft 4.

The compactness of the improved pump is enhanced due to the fact that the housing 1 constitutes the case or housing for the impeller 25 of the centrifugal pump. The impeller 25 may form an integral part of the shaft 4. The inlet 29 can be omitted if the pump is installed directly in an oil tank, i.e., the pump then draws liquid directly by way of the axial bore 27 in the shaft 4, and the end portion of the shaft then constitutes an inlet. The impeller is preferably provided on that portion of the shaft 4 which is located between the eccentric 7 and the output shaft of the motor which drives the pump.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applyingcurrent knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of the above-outlined contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claim.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claim.

We claim:

1. In a radial piston pump, a combination comprising a housing defining a compartment and having a liquid admitting inlet; a driven shaft journalled in said housing and having eccentric means; a cylinder block provided on said housing, said block having an outlet and conduit means connecting said compartment with said outlet; normally closed suction valve means provided in said conduit means; a centrifugal pump member driven by said shaft to draw liquid from said inlet into said compartment and to force liquid to fiow into said conduit means towards said valve means, said centrifugal pump member comprising an impeller eccentrically mounted on said shaft to balance said eccentric means; and a piston received in said block and reciprocable by said eccentric means to intermittently open said valve means and to effect the flow of liquid into said outlet.

References Cited UNITED STATES PATENTS 2,605,707 8/1952 Worlidge 103-174 2,394,285 2/1946 Bevins 103-174 2,612,837 10/1952 Midgette 103-174 2,693,150 11/1954 Pickard et al. 103-174 2,851,952 9/1958 Lane 103-174 2,865,292 12/1958 Raibaud 103-171 3,125,034 3/ 1964 Lucien et al. 103-174 WILLIAM L. FREEH, Primary Examiner U.S. Cl. X.R. 417-273, 570 

